Enhanced boiling heat transfer of HFE-7100 on copper foams under overflow conditions

Abstract

Boiling of dielectric liquids on structured surfaces is a powerful option for thermal management of electronic devices, whose cooling performance depends strongly on liquid supply and vapor departure. Herein, saturation boiling of HFE-7100 on copper foams with a pore density of 30 pores per inch (PPI) under overflow conditions is proposed to enhance liquid supply and facilitate vapor departure. Liquid HFE-7100 is fed to the copper foam by a peristaltic pump and un-vaporized liquid is discharged by gravity. The higher flowrate leads to higher critical heat flux (CHF) and heat transfer coefficient (HTC) only if the copper foam is not flooded. Visual observations reveal evolution of vapor bubbles with heat flux on the copper foam under overflow conditions. Dependence of CHF and HTC on foam thickness is experimentally evaluated and an optimal thickness of 4.7 mm is derived from the experimental data. The optimal foam thickness is related to submergence level of bulk flow and capillary height. CHF and HTC are enhanced by the forced liquid supply in combination with the reduced hindrance of hydrostatic pressure to vapor departure, reaching 860 kW m−2 and 47.3 kW m−2 K−1, respectively. The overflow boiling offers an efficient way to improve heat transfer of boiling on porous medium for efficient thermal management.